This application claims the priority of German Application No. 199 54 652.5 filed Nov. 13, 1999, which is incorporated herein by reference.
This invention relates to a method of internally coating a weapon barrel. Conventionally, for preventing erosions of the weapon barrel, a cover layer of high melting point and composed of at least one material is applied by electroplating to an axial length portion of the inner barrel surface.
The firing of power-enhanced ammunition from large caliber, smooth-barrel weapons leads to prematurely strong wear of the inner barrel surface because of the high gas temperatures and flow velocities that occur during firing.
For avoiding the above-noted wear phenomena, it has been known to provide the inner weapon barrel surface with a hard chromium layer by electrolytical deposition. In most instances, however, the relatively brittle, hard chromium layers of power-enhanced ammunition applied according to the known processes do not adhere in a satisfactory manner to the barrel surface so that partial peeling of the regions provided with the chromium layer occurs. As a result, the barrel material is, in such regions, exposed to the hot combustion gases, and strong, erosion-caused wear of the barrel material occurs. Further, the substantial heating of the chromium layer upon firing of the ammunition may result in an unintentional local fusion of the chromium on the weapon barrel.
It is an object of the invention to provide an improved method of internally coating a weapon barrel with a galvanically applicable cover layer which results in a coating that prevents an erosion-caused wear of the barrel even upon firing power-enhanced ammunition.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the method of coating an internal surface of a weapon barrel includes the steps of applying an intermediate layer to the internal barrel surface by explosion plating and applying a cover layer at least indirectly (that is, either directly or with the interposition of a further layer or layers) to the intermediate layer by electroplating. The intermediate layer has a heat conductivity which is greater than that of the weapon barrel and a ductility which is greater than that of the cover layer.
The invention is based essentially on the principle to apply to the inner surface of the weapon barrel an intermediate layer by means of explosion plating prior to applying the cover layer by electroplating. While the cover layer has the purpose of protecting the barrel material (and thus also the intermediate layer) from high gas temperatures and preventing a thermo-chemical reaction between the layer combination and the combustion gases upon firing the ammunition, the intermediate layer, based on its high heat conductivity, is intended to rapidly lower the peak temperature in the cover layer and in the surface region of the weapon barrel. For this purpose, the heat conductivity of the intermediate layer has to be greater than that of the barrel material. Further, the intermediate layer should have a higher ductility as compared to the cover layer and should prevent a spreading of fissures which appear in the cover layer so that the maximum expansion capacity of the layer combination is increased.
As materials for the cover layer pure metals, metal alloys or dispersion-reinforced metals and/or metal alloys may be used as long as they have a high melting point (preferably equal to or above 1600xc2x0 C.) and are sufficiently inert to combustion gases. Chromium has been proven to be particularly advantageous as such a coating material.
The intermediate layer should be a metallic material having a high heat conductivity (preferably equal to or greater than 90 W/mK), a high ductility and a sufficient strength. In this respect pure metals, metal alloys or dispersion-reinforced metals and/or metal alloys may be considered. Copper, nickel and cobalt as well as alloys of these metals have been found to be particularly advantageous as materials for the intermediate layer.
As compared to a conventional galvanic hard chromium coating, the method according to the invention excels particularly in that based on the superior heat conductivity of the explosion-plated intermediate layer, the peak temperature in the galvanically deposited cover layer may be lowered rapidly. As a result, the thermal, thermo-mechanical and thermo-chemical stresses on the cover layer are significantly reduced. Further, the peak temperature in the boundary layer to the barrel material is reduced because of the greater total layer thickness as compared to the conventional galvanic hard chromium layer.